Abstract

We present a theoretical model for metal-cavity submonolayer quantum-dot surface-emitting microlasers, which operate at room temperature under electrical injection. Size-dependent lasing characteristics are investigated experimentally and theoretically with device radius ranging from 5 μm to 0.5 μm. The quantum dot emission and cavity optical properties are used in a rate-equation model to study the laser light output power vs. current behavior. Our theory explains the observed size-dependent physics and provides a guide for future device size reduction.

(a) Wavefunctions of the first two conduction band states (CB1 and CB2) and the first two heavy-hole states (HH1 and HH2). The wavefunctions are shown at the isosurface of
|Ψ|2=0.5|Ψ|max2. The blue disks are the 10-fold vertically-correlated submonolayer quantum dots, assuming no lateral coupling. (b) Wavefunction of the conduction band ground state (CB1), considering lateral coupling. The wavefunction is shown at the isosurface of
|Ψ|2=0.16|Ψ|max2. In this example, the quantum-dot 2D fill factor is 62.8% and the 2D dot density is 2 × 1011 cm−2.

(a) Ground state transition energy as a function of the temperature for different effective dot sizes. The measured photoluminescence peak is shown as the star. [8] (b) The quasi-Fermi level Fc for conduction band (blue circles) as a function of injected carrier density. Horizontal lines show 50 conduction band states with bound states circled. (c) The quasi-Fermi level Fv for valence band (red circles) as a function of injected carrier density. Horizontal lines show 50 heavy-hole and 20 light-hole states.

(a) Calculated lasing wavelength and the photon lifetime as a function of the cavity diameter for the fundamental HE11 transverse mode. (b) Calculated cavity quality factor and effective mode volume as a function of the cavity diameter for the HE11 transverse mode.

(a) Calculated Purcell factor for the fundamental mode in the metal-cavity micro-lasers with different cavity diameters. (b) Extracted spontaneous emission coupling factor βsp from the fitting of device light output power vs. current (L-I) curves with the rate-equation model.